情态动词一些用法（内部使用） 句式形 式意 思例 句备 注对现在动作的揣测肯定1） must be…2） may/might be…1肯定是…2也许是…This must be your pen .He may be very busy now.1 must be doing sth (一定在做某事)He must be waiting for us.否定can’t / couldn’t be…不可能是...He can’t/couldn’t be a spycouldn’t语气更婉转，更不可能 疑问Can/Could…be..? 可能是…?Can this be true ?could语气更婉转，可能性更小对过去或现在成完动作的揣测肯定1) must have done sth2) may/might have done sth1肯定已做某事2也许已做某事1) He must have arrived at the airport by now.2) He may/might have finished the work.1) might语气更婉转，实现的可能性更小 2) must have been doing sth(肯定已在做某事)否定1) can’t/couldn’t have done sth2) may/might not have done sth3) can’t/couldn’t have been doing sth1不可能已故做某事2也许没做某事1) He can’t/couldn’t have phoned you because he didn’t know your telephone number.2) My father may/might not have finished his work.3) All the lights were out.They couldn’t have been working in the factory.. 1．couldn’t have done sth语气更加婉转，不肯定。
疑问Can/Could….have done sth ?可能已做某事Can/ Could he have found the book?其它用法肯定should/ought to have done sthcan/could have done1本应该做某事2本能做某事She should /ought to have finished her work by now.1）过去应该做而实际未做2）过去本可能做某事但未做否定1) needn’t have done sth2) shouldn’t/oughtn’t to have done sth1．本没必要做某事2.本不应该做某事1) You needn’t have watered the flowers, for it is going to rain. 2) She shouldn’t/oughtn’t to have taken away my measuring tape, for I wanted to use it.1本不必做而实际上做了2本不应该做而实际上做了。